Railway operations are usually controlled and monitored using signal cabins which ensure the safety of the railway traffic. To do this, the signal cabins use a very wide range of track sensors to monitor the locations of the trains moving in the area which they control, and ensure, by means of light signals, that successive trains do not come dangerously close to one another. In addition, signal cabins are used to switch routes for the trains, opposing moves or slanting moves being reliably avoided by means of exclusion and logic-linking procedures. The trains automatically release the parts of the route which they have cleared behind them and these parts of routes available again for the controlling and monitoring signal cabin.
Signal-cabin-controlled railway operations are appropriate to use on routes along which multiple trains are intended to travel with the greatest possible density and at the highest possible speed. Signal cabins are indispensable for controlling railway traffic on main routes. However, they require a system on the tracks for determining the position of the vehicles and a centralized system for signaling proceed aspects or travel instructions to the trains.
In order to limit the expenditure involved in determining the locations of the trains and signaling travel instructions, decentralized train protection systems, which permit safe journeys without the use of signal cabins have recently been preferred for routes with moderate traffic. In these decentralized train protection systems, the trains traveling along the route determine their respective location and transmit the location to decentralized devices along the route. These devices are commonly referred to as track area elements.
Devices along the route are preferably assigned to switches and are addressed by the trains by means of telegrams. The trains register their request to be allowed to travel along the route with the devices using telegrams. The devices along the route check whether there are already applications for opposing moves in the respective route section or whether approvals have already been given for such moves. If this is the case, the request by the vehicle wishing to travel along the route cannot be granted, in which case a message to this effect is transmitted to the requesting vehicles. The vehicle must subsequently stop no later than the point on the route up to which it still has permission to move forward. However, if at the time a train makes a request to a device along the route there has not been any request to the device to assign the route which it administers (or parts of the route) to a train which is moving forward in the opposite direction, and if a corresponding approval to travel along the route in the opposite direction has not been granted, the device along the route accepts the request originating from the train and assigns permission to the train to travel along the route which it administers. A prerequisite is that the permission to travel along the route has not already been assigned to a train located ahead of the train or that an older request for the assignment of permission to travel along the route is present from there. Permission to travel along the route administered by a device along the route can only be assigned to just one train by each of the devices along the route, a following train cannot travel on the route until the train ahead has completely cleared the route. Opposing moves on the route are not possible until all the trains traveling on this route in the assumed direction have cleared the route administered by the device along the route. In the statement above it has been assumed that between the trains moving in the assumed direction of travel toward the devices along the route there are no branches at which, for example, following trains can leave the track on which more than one train is traveling.
Vehicles moving along the route determine their respective location along the route, for example using GPS systems, and transmit to the devices along the route appropriate location messages from which devices can determine whether the route sections locked out for the trains are still being traveled along or have already been cleared. In the latter case, a request by another train for assignment of permission to travel along the respective route can then be processed, and, if appropriate, granted. The devices along the route have sufficiently precise information on the location of the route sections occupied by the individual trains if, in addition to appropriate locating information being transmitted by the trains, it is also certain that the trains are complete (i.e. include their usual number of cars). The trains must check this complete state continuously or at least at predefined chronological or spatial intervals and either transmit appropriate messages to the devices along the route or include these messages in the location messages in some suitable way. The devices along the route then take into account, for the protection of the route, either the actual length of the trains or else they take into account standardized length values.
In order to, if appropriate, make multiple requests for permission to travel along certain route sections, to continuously transmit permission messages to the vehicles and to continuously transmit location messages so that route sections which have already been cleared are made available at an early point, it is necessary to have very intensive data traffic between the trains and the devices along the route. This data traffic becomes more complex as the number of vehicles or trains passing through the route per time unit increases, the more frequent the updating of the location messages and the greater the precision with which the route is to be subdivided in a virtual fashion in order to maintain intervals between successive trains.